For example, RFID (Radio Frequency Identification) is widely known as a technique for reading and writing data from and into an IC chip incorporated in a data carrier (RF tag, IC tag, or ID tag) by performing near field radio commutation.
RFID can be roughly divided into radio wave RFID and magnetic field (electromagnetic induction) RFID depending on a method of transmitting data. In the radio wave RFID, a radio wave carrying data is exchanged between an antenna of a reader-writer and an antenna of a data carrier. In the magnetic field RFID, a coil antenna of a reader-writer and a coil antenna of a data carrier are coupled by electromagnetic induction and data is thus exchanged between the reader-writer and the data carrier.
The radio wave RFID and the magnetic field RFID each have advantages and disadvantages.
The radio wave RFID has advantages such as relatively low production cost and high versatility. Moreover, since electric power can be generated in the data carrier by rectification, the data carrier can be formed as a passive tag which needs no power supply (battery). On the other hand, the radio wave RFID has disadvantage that, when a long communication distance is set, the reader-writer communicates not only with a specific data carrier but also with data carriers in the periphery of the specific data carrier. Furthermore, the radio wave RFID tends to be affected by reflection of the radio wave on a metallic surface and absorption of the radio wave by water, and also has a problem of regulation by the radio law, a problem of interference with other radio devices, and other problems.
The magnetic field RFID has an advantage that it is less likely to be affected by dusts and the like and can be used in a poor surrounding environment. Moreover, since electric power can be generated in the data carrier by resonance, the data carrier can be formed as a passive tag, as in the radio wave RFID. On the other hand, the magnetic field RFID has disadvantages that a communication distance is short and the reader-writer and the data carrier have to be accurately positioned relative to each other for the electromagnetic induction coupling. Moreover, the magnetic field RFID has a disadvantage that, since the frequency is low, the communication speed is low.